In recent years, photofabrication of three-dimensional objects consisting of cured resin layers integrally laminated by repeating a step of selectively irradiating a photocurable liquid material (photocurable resin composition) has been proposed (see Japanese Patent Applications Laid-open No. 247515/1985, U.S. Pat. No. 4,575,330, No. 35966/1987, No. 101408/1987, and No. 24119/1993).
A typical example of the above photofabrication process is as follows. A cured resin layer having a specified pattern is formed by selective exposure to radiation such as from an ultraviolet laser on the surface of the photocurable resin composition in a vessel. An amount of the photocurable resin composition equivalent to another layer is then provided over this cured resin layer followed by selective irradiation to the liquid surface to form a new cured resin layer integrally laminated over the primary layer. The above step using the same or different irradiated patterns is repeated certain times to obtain a three-dimensional object consisting of a plural integrally-laminated cured resin layer. This photofabrication process has attracted considerable attention, since three-dimensional objects having a complicated shape can be easily formed in a short time by using this process.
As the photocurable resin composition used in this photofabrication of three-dimensional objects, the following resin compositions (a) to (c) have been conventionally proposed:
(a) a resin composition containing a radically polymerizable organic compound such as urethane (meth)acrylate, oligoester (meth)acrylate, epoxy (meth)acrylate, thiol, ene compound, and photosensitive polyimide (see, for example, Japanese Patent Applications Laid-open No. 204915/1989, No. 208305/1990, and No. 160013/1991); PA1 (b) a resin composition containing a cationically polymerizable organic compound such as an epoxy compound, cyclic ether compound, cyclic lactone compound, cyclic acetal compound, cyclic thioether compound, spiro orthoester compound, and vinyl ether compound (see, for example, Japanese Patent Application Laid-open No. 213304/1989); and PA1 (c) a resin composition containing both a radically polymerizable organic compound and a cationically polymerizable organic compound (see, for example, Japanese Patent Applications Laid-open No. 28261/1990, No. 75618/1990, and No. 228413/1994). PA1 (A) a cationically polymerizable organic compound; PA1 (B) a cationic photopolymerization initiator; PA1 (C) an ethylenically unsaturated monomer; PA1 (D) a radical photopolymerization initiator;and PA1 (E) a polyether polyol compound having one or more hydroxyl groups in one molecule.
In view of efficiency of the photofabrication, the photocurable resin composition used in the photofabrication is required to exhibit low viscosity for immediately forming a smooth liquid surface and high curability by exposure to radiation, and the resulting cured product consisting of the three-dimensional objects is required to exhibit no swelling and minimal deformation such as warping, indentation, and overhanging of the stretched part caused by shrinkage during curing by exposure to radiation. Moreover, superior stability with time of these mechanical properties are required for such objects.
The three-dimensional objects formed by the photofabrication are used for design models, prototypes of mechanical parts, and the like. In particular, when these three-dimensional objects are used for prototypes of mechanical parts, such objects have to be formed by high-precision microfabrication conforming to specified procedures and exhibit sufficient mechanical strength, superior heat resistance, and excellent waterproofing characteristics under use conditions.
However, no conventional resin composition can satisfy the above demands. Three-dimensional objects formed by photofabricating the above-described conventional resin compositions exhibited deformation with time such as warping, indentation, and overhanging of the stretched part due to residual distortion caused by the shrinkage during curing. When the resin composition (a) containing a radically polymerizable organic compound such as urethane (meth)acrylate, oligoester (meth)acrylate, epoxy (meth)acrylate, thiol, ene compound, and photosensitive polyimide is used as the photocurable resin, although the resulting three-dimensional objects exhibit relatively excellent mechanical properties, it has been pointed out that further improvements are required to minimize inaccuracy of fabrication and variation with time of the fabricated forms (Journal of Fabrication, vol. 9, No. 5, pp. 330-335, 1997). In order to increase accuracy of fabrication, a method for controlling phototransmission depth of the resin composition by blending core-shell composite polymer particles (see Japanese Patent Application Laid-open No. 114733/1991) or particles consisting of polarizing materials having a refractive index essentially differing from that of the resin composition (see Japanese Patent Application Laid-open No. 103415/1991) by utilizing diffusion of light has been proposed. However, sufficient accuracy of fabrication has not been achieved by using such a method.
When the resin composition (b) containing a cationically polymerizable organic compound such as an epoxy compound, cyclic ether compound, cyclic lactone compound, cyclic acetal compound, cyclic thioether compound, spiro orthoester compound, and vinyl ether compound is used as the photocurable resin, fabrication cannot be carried out efficiently due to insufficient curablity of the composition. The three-dimensional objects formed from the resin composition (b) exhibit relatively higher accuracy of fabrication. However, because mechanical properties of the resulting three-dimensional objects deteriorate with time depending on the working conditions (temperature and humidity), such objects cannot be used under the conditions where long-term mechanical strength is required. Moreover, it has been pointed out that these objects cannot be used practically as functional parts because of insufficient mechanical strength, in particular, insufficient toughness such as low impact resistance and low folding endurance.
In view of the above situation, the resin composition (c) containing both a radically polymerizable organic compound and a cationically polymerizable organic compound has been proposed. Although curability of the composition is improved to a certain extent, the objects formed from the composition cannot be used in practice because of inadequate mechanical properties, in particular, insufficient toughness.
In order to provide three-dimensional objects with mechanical strength, toughness in particular, a resin composition containing microparticles with a specific gravity differing from that of the resin composition in a range within 0.2 has been proposed (see Japanese Patent Application Laid-open No. 145616/1990). In spite of increased toughness of the resulting three-dimensional objects, such objects exhibited weak folding endurance during repeated foldings when used as functional parts.
The present invention has been achieved based on the above situation.
An object of the present invention is to provide a novel photocurable liquid resin composition.
A second object of the present invention is to provide a photocurable liquid resin composition used for photofabrication of three-dimensional objects which exhibit superior mechanical strength and high dimensional accuracy and are suitably used as prototypes for mechanical parts and the like.
A third object of the present invention is to provide a photocurable liquid resin composition used for photofabrication of three-dimensional objects exhibiting small deformation with time.
A fourth object of the present invention is to provide a photocurable liquid resin composition used for photofabrication of three-dimensional objects exhibiting small variation of mechanical properties with time.
A fifth object of the present invention is to provide a photocurable liquid resin composition used for photofabrication of three-dimensional objects exhibiting superior mechanical properties, in particular, high toughness such as high impact resistance.
A sixth object of the present invention is to provide a photocurable liquid resin composition used for photofabrication of three-dimensional objects exhibiting high folding endurance.
A further object of the present invention includes those wherein the photofabrication composition is transparent before cure and/or after cure.